Plants of Southern California: Ribes indecorum and R. malvaceum

Fig. 1.
Top. Photographs from the Spitler Peak Trail on 29 March 2018 from a population of ~150 plants consisting of plants with only white flowers and plants with only pink/red flowers. Left: photograph of a white Ribes flower that would presumably be determined as R. indecorum. Right: photograph of a pink Ribes flower that would presumably be determined as R. malvaceum. However, both of these plants are actually R. malvaceum; see Plants of San Jacinto Mountain: Ribes malvaceum.

Bottom. Left: photograph of one of the flowers on Cahuilla Mountain on 9 April 2018, from a population of over 100 plants which all had white flowers. Right: photograph of one of the pink flowers on the Ramona Trail on 3 April 2018, from a population of ten plants, of which half had only white flowers and half had only pink/red flowers. The flowers from these two locations have essentially-identical measurements for the characteristics used in the Flora of North America key except for the color of the flower.

The problems in these Ribes taxa almost surely derive from the lack of any recent critical study of these taxa. The only monographs on Ribes are by Janczewski in 1907, and Berger in 1924, when the number of vouchers of each species were few, making it difficult to know the range of variability of each supposed taxon. Only one subgroup of Ribes has a recent monograph, for section Grossularia by Sinnott 1985, which does not include any of these species.

Interestingly, Janczewski considered R. indecorum to be the same species as R. malvaceum, giving R. indecorum as a synonymous species to R. malvaceum. I haven't been able to get a copy of Berger, but presumably he must have separated them again.

On the face of it, it should be exceptionally easy to separate R. indecorum and R. malvaceum. Here is the Munz 1974 key:

Early in my botanical career I only found populations with pure white flowers, so it seemed that this was not only a simple key, it was an accurate key.

But then in 2004, I saw plants on the Stunt Road Trail to Saddle Peak in the Santa Monica Mountains, and found plants with white flowers totally intermixed with plants with pink flowers. I wrote:

Ribes indecorum, R. malvaceum var. viridifolium. The plants on this trail are so similar it is quite understandable that the Santa Monica Mountain (SMM) Flora lists R. indecorum as a subspecies of R. malvaceum. The only clear difference is the color of the sepals.

The SMM Flora says that intergrades between the two species occur, but it is difficult to detect them without detailed analysis. In particular, the JM criterion on the length of the hypanthium is not a good discriminant, since many pure plants of R. indecorum have a hypanthium twice as long as wide (see Munz).

In that comment, I was referencing the previous version of the SMM flora by Raven et al. There is now a newer version by Prigge and Gibson; see below.

Subsequently, I saw many populations in other areas that had only white flowers, and other populations that had just pink or reddish flowers, and I gradually forgot that the populations were intermixed in the SMM. Even if I had remembered that, I perhaps would have just thought that the SMM might be an area where the two species intergrade.

In 2018, Bruce Watts observed a population of ~150 plants along the Spitler Peak Trail above Garner Valley in the San Jacinto Mountains, where plants with white flowers were intermixed with plants with pink / red flowers. I went with Bruce to see this population, and it seemed clear in the field there was only a single species here, with flowers that varied from pure white to deep pink/red. It did not surprise me to find white flowers with the pink/red flowers, since nearly every species has a white color variant. It would be surprising if there were not a white variant of R. malvaceum, which could still be different from R. indecorum.

Bruce and I returned to the Spitler Peak Trail on 14 April 2018, and it was clear from field observations and measurements on the flowers that all the plants on the Spitler Peak Trail, the white-flowered plants and the pink/red-flowered plants, were R. malvaceum. See Plants of San Jacinto Mountain: Ribes malvaceum.

It was interesting that when Bruce first saw the plants, ~90% of the flowering plants had white flowers. When we saw the plants together later, something like 90% of the flowering plants had pink / red flowers. So there is a slight difference in flowering time between the color variants.

I then found the Flora of North America (FNA) key and descriptions that provided other characteristics to separate the species. The separating characteristics, from the key and descriptions, are:

With such wonderfully-clear numerical distinctions, I was then anxious to measure some flowers from the San Jacinto Mountains (SnJt) to see where they fell.

I was hoping to find some clear R. indecorum for comparison, so I next went to the Ramona Trail on the south side of Garner Valley. There were only about ten isolated plants there, five with only white flowers, and five with only pink flowers. I expected that these, too, would fall with R. malvaceum. The measured characteristics for the white flowers were the same as the measured characteristics for the pink / red flowers, making it very unlikely these were different species.

But to my surprise, these plants clearly did not fit R. malvaceum, having significantly shorter hypanthium, filament and style lengths, and a sepal length that is uncommon for R. malvaceum. They equally had problems fitting the R. indecorum description, with the wrong hypanthium color and style hairiness, and longer sepals and filaments.

I next went to Cahuilla Mountain, and found a population of well over 100 plants that all had white flowers, and thus would appear to be pure R. indecorum. However, again to my surprise, the measured characteristics of those flowers was essentially identical to those of the plants on the Ramona Trail.

So there seems to be something interesting going on with these two species beyond that stated in the floras. I do not by any means understand what is going on with these two species. Possibilities range from the two species not actually being separate taxa, to the two species simply needing to have their descriptions amended to include more variability. More study is needed!

The rest of this page presents the measurements made on the flowers from the Ramona Trail and Cahuilla Mountain, and the comparison to the FNA descriptions. For measurements on the Spitler Peak population, see Plants of San Jacinto Mountain: Ribes malvaceum.

Prigge and Gibson have made detailed measurements separately on the white and pink/red flowered plants in the Santa Monica Mountains. Interestingly, they note the same flowering time difference between the plants with white flowers and those with pink/red flowers! They state that "Ribes indecorum closely resembles the more common R. malvaceum but differs in having white flowers; R. indecorum commonly begins flowering several weeks earlier". They note that their measurements for R. indecorum are also not consistent with "existing descriptions of R. indecorum in southern California". This page also presents their measurements for comparison to the SnJt plants.

Characteristics of the San Jacinto Mountain area plants

Four of the measured characteristics of the plants from the Ramona Trail and Cahuilla Mountain are presented in Fig. 2, separated by the color of the flowers.

Fig. 2. Top: Sepal length vs. hypanthium (free portion) length. Bottom: Filament length vs. style length. The population labeled as white are from Cahuilla Mountain, where all the plants have only white flowers. The other two populations are from the Ramona Trail, where there are plants that have only white flowers, labeled White (in pink pop), and plants that have flowers that are white and pink, labeled White / pink.

There is no difference in the measured values between the white flowers and the pink/red flowers, with the exception that the filaments for the white flowers are possibly very slightly shorter.

These characteristics do not fit either species well. Although the measurements for these four characteristics are closer to the values for R. indecorum, the pink/red color of many of the flowers, and the spreading hairs on the style, make it impossible to say that these plants are closer to either species.

Characteristics of the Santa Monica Mountain plants

The wonderfully-detailed description of the plants in the Santa Monica Mountains by Prigge and Gibson are given online here: R. indecorum and R. malvaceum.

Prigge and Gibson give direct measurements for all the characteristics mentioned above except for the style length for R. malvaceum. They give measurements for the pistil length and ovary length, so I derived measurements for the style by subtracting the ovary length from the pistil length, which should be approximately correct since the stigmas are very short.

Fig. 4 plots the SMM values against the FNA values.

Fig. 4. Top: Sepal length vs. hypanthium (free portion) length. Note the large amount of overlap in the lengths for the two species. Bottom: Filament length vs. style length. Note the strong overlap in the filament lengths for the two species.

The SMM measurements are clearly also very different from the FNA values. They are also different from the measurements of the SnJt plants; see Fig. 5.